Sexually transmitted infections are infectious diseases that are transmitted from infected to a healthy person by sexual contact; still, it can also be transmitted through indirect contact and from mother to child. The infectious agents can be different microorganisms belonging to bacteria, viruses, fungi and parasites. These are the most important public health challenges. Sexual diseases are a very big problem for the whole population, especially in the younger population. Every year there is an increase in the number of people infected because of an accelerated lifestyle, an early age for sexual intercourse, frequent partner changes, under-utilization of health care, sexual activity without preventive protection, failure to follow treatment instructions and failure to include escorts in treatment, and recklessness about the consequences it causes risky sexual behaviour. The term sexually transmitted diseases (STDs) mean infectious diseases that are transmitted through direct contact during sexual intercourse. Transmission of STDs can be oral, vaginal or anal intercourse. Due to the high incidence and development of the disease, STDs represent a huge problem among young people all over the world, including in Croatia. Sexuality of children and adolescents in Croatia is still considered a provocative topic and STDs are a significant global problem that needs to be addressed by educating young people about prevention. Human immunodeficiency virus (HIV)was unknown until the early 1980s, but has since infected millions in the worldwide pandemic. By the end of the 20th century, more than 21 million people worldwide had died of AIDS. The cornerstone of HIV control and prevention it the population is knowledge of HIV as a sexually transmitted disease. Unfortunately, most people are unaware of their HIV status (fear of positive results, individual’s education level, stigmatization and discrimination of HIV/AIDS). Various studies conducted in developed countries have shown that knowledge of HIV status can reduce highrisk sexual practices and reduce the rate of spread in terms of prevention. When it comes to the prevention of sexually transmitted diseases, education is of paramount importance, especially among the younger population.